Question: On the first 3 exams of her physics class, Gabriela got an average score of 79. What does she need on the next exam to have an overall average of 82?
Solution: Let her score on the next exam be $x$ The sum of all of her scores is then $3 \cdot 79 + x$ The same sum must also be equal to $4 \cdot 82$ Solve: $x = 4 \cdot 82 - 3 \cdot 79 = 91$.